Bicycle shock absorbers are designed to soften the effect of bumps and holes in the roadway as impacted on the rider. The shock absorption feature is typically provided in the bicycle's front wheel steering fork. When the front wheel falls into a hole or hits a bump, the wheel is jarred or jolted and (without the shock absorbers) the shock effect is transferred through the front wheel support and steering mechanism (the steering fork) directly to the rider, i.e., to his arms particularly when he is leaning forward as in racing, but also to the rider's torso supported on the pedals and seat of the bicycle. Shock absorption for the fork is provided by having collapsible struts that collapse against an elastic member, e.g., a spring member. Thus, the shock is "absorbed" by the elastic member and the jarring action is converted to a softer bouncing-like action.
Whereas this bouncing-like action is far easier on the rider than the jarring effect without the shock absorbers, there is the problem of setting in motion a repetitive cycling of the bouncing action as the elastic member compresses and expands in seeking its equilibrium. The repetitive bouncing is not desirable and, thus, shock absorbers of the type herein contemplated are provided with a damping feature. A damping feature functions in concert with the elastic member by permitting but resisting the compression and expansion cycles and more rapidly causes the elastic member to find the equilibrium position.
Typically dampers for shock absorbers have been provided using liquid, (e.g., oil) that is sealed inside the fork and through design is moved back and forth between two chambers through a restricted portal as the elastic member is compressed and expanded. The portal allows liquid flow therethrough but resists rapid movement of the liquid. The effect is that the initial jarring action produces sufficient force on the liquid to rapidly (but less rapidly than without the restriction) transfer the liquid to the other chamber. Then as the elastic member tries to rebound or expand, that movement is also resisted by requiring reverse flow of the liquid through the portal. The result is that repetitive bouncing is retarded.
The problems associated with liquid (oil) dampers is that total sealing is difficult to maintain and, thus, leaking frequently occurs, and the oil gets hot and less viscous when in constant activity and this affects resistance and retardation of the bouncing. Further, air weighs less than liquid and even small weight reduction is considered important for bicycles.